Conventionally, for example, a technique of applying a hologram on a surface of an article, and a technique of applying special ink on a surface of an article have been known as anti-falsification methods for articles, for example, for cards and security notes. In addition, a technique of randomly mixing a detectable material such as magnetic powder, magnetic fiber, metallic powder, or a metallic fiber in a paper has been known as anti-falsification methods. In the technique in which the hologram is used, the authenticity of the article on which the hologram is applied is determined by viewing the hologram, which appears to be three-dimensional or varies in color depending on the viewing angle. In the technique in which the special ink is used, for example, fluorescent ink or magnetic ink may be used as the special ink. The authenticity of the article on which the above ink is applied is determined by detecting information hidden in the above ink by irradiating ultraviolet light thereon or by magnetic sensors, although the above ink may be viewed in the same manner as normal inks. In the technique in which a paper is used in which the above detectable material is randomly mixed, an individual distribution pattern thereof is recorded beforehand, and the authenticity of the article is determined by detecting a distribution pattern thereof when it is used again, and then by comparing it with the recorded pattern.
In Patent Publication 1, a falsification technique is disclosed in which a cholesteric liquid crystal is combined with a hologram. In this technique, a color change of the cholesteric liquid crystal which depends on the viewing angle is used together with a latent image of the hologram which changes depending on the viewing angle thereof. Alternatively, a reflecting characteristic of circular polarization of the cholesteric liquid crystal, in which left-handed circular polarization light or right-handed circular polarization light is selectively reflected and the reflected light has the same circular polarization direction as the incident light, is used together therewith. In Patent Publication 2, a technique is disclosed in which a characteristic of a cholesteric liquid crystal reflecting a specific circular polarization light and a characteristic of changing wavelength of the reflected light depending on the viewing angle are used.
However, the above falsification techniques have become more sophisticated as hologram manufacturing techniques have come into wider use, it is easy to falsify the hologram, and the falsified hologram cannot thereby be distinguished from an authentic one. Although the technique using the fluorescent ink or the magnetic ink, or the paper into which the detectable material such as magnetic powder, magnetic fiber, metallic powder, or metallic powder is mixed, is difficult to be falsified, a device for sensing information hidden in the above inks and a device for detecting the distribution pattern on the above paper are very large and require a power supply. Therefore, the above technique cannot be used when easy execution is required. In the techniques in which the cholesteric liquid crystal is used together with the hologram, more complicated structures have been required as hologram manufacturing techniques have come into wide use. Anti-falsification techniques are required in which it is difficult to falsify a discrimination medium and which facilitate determining the authenticity of the discrimination medium.
In the Patent Publication 1, the cholesteric liquid crystal is used together with the hologram, refleced light therefrom is observed through a left-handed circular polarization light filter and a right-handed circular polarization light filter. For example, when the reflected light therefrom can be seen through a left-handed circular polarization light filter, the reflected light therefrom cannot be seen through a right-handed circular polarization light filter. By using this phenomenon, the authenticity of discrimination medium is determined. However, in the above manner, one portion of the discrimination medium turns black and only the image at the portion cannot be seen, so that falsified articles may produced by employing circular polarization light filters.
In the Patent Publication 2, when a discrimination medium having two laminated pieces of cholesteric liquid crystal is viewed through liquid crystal filters having the same characteristics, the discrimination medium changes in color depending on the liquid crystal filter corresponding thereto. By using this phenomenon, the authenticity of the discrimination medium is determined. However, a simple determination tool having the same liquid crystal as the above cholesteric liquid crystal is not widely used, so that a test apparatus is required in accordance with the cholesteric liquid crystal.
The Patent Publication 1 is Japanese Patent Application Publication No. Hei 9-319566. The Patent Publication 2 is Japanese Unexamined Patent Publication No. Hei 11-42875.